1. Field of the Invention
The present invention relates to a method and an apparatus for bonding a flexible board, and more particularly, to a method and an apparatus for bonding a flexible board suitable for bonding a flexible printed circuit board to a head holding member that constitutes a magnetic head (for a hard disk drive apparatus).
2. Related Background Art
In conventional magnetic heads for use in hard disk drives, lead wires are drawn out via an electrode pad from the slider side in which an MR element etc. are built in, and the lead wires are soldered to a flexible printed circuit board to allow signal input and signal output through the slider side.
However, in magnetic heads in recent years, with downsizing of sliders or the use of negative pressure sliders, the force for pressing a recording medium (so-called load pressure) has become extremely low. As a result, the above-described structure might suffer from the problem that the aforementioned force for pressing a recording medium can vary depending on the rigidity of the lead wires.
In order to solve this problem, there has been known a method in which the slider and the flexible printed circuit are electrically connected directly without using a lead wire.
FIG. 6 is a perspective view showing how a flexible printed circuit board is bonded to a head holding member.
As shown in FIG. 6, a head holding member 1 that constitutes a magnetic head is provided with a flexible member (or a flexure) 3 disposed between a load beam 2 and the aforementioned slider. The flexible member has elasticity to ensure a degree of freedom of the slider. A flexible printed circuit board 5 is bonded to the head holding member 1 having the above-described structure along the direction indicated by an arrow 4.
In the process of bonding the aforementioned flexible printed circuit board 5 to the head holding member 1, the flexible printed circuit board 5 arranged on a tray is first sucked by a suction head by area A shown in FIG. 6, and the suction head is then moved to a position above the head holding member 1 placed on a support table for bonding while maintaining the suction. After the flexible printed circuit board 5 is moved to the position above the head holding member 1, the suction head is lowered, so that the flexible circuit board 5 is bonded to one surface of the head holding member 1 on which an adhesive has been attached in advance. Alignment of the flexible printed circuit board 5 relative to the head holding member 1 is generally carried out using image processing. Specifically, when the flexible printed circuit board 5 is moved while maintained in a suctioned state, a center hole, for example, of the flexible printed circuit board 5 is detected by a CCD or the like and its positional difference relative to the head holding member 1 set on the support table is calculated. Thus, bonding is carried out after the position of the suction head has been aligned with the position of the head holding member 1.
A suction head as shown in FIG. 7 has also been known as one to be used in bonding a flexible printed circuit board (see FIGS. 1 and 2 of Japanese Patent Application Laid-Open No. 2002-288812).
As shown in FIG. 7 which shows the cross sectional structure of a suction head, the suction head 6 is provided with suction ports at positions corresponding to both end portions of a flexible printed circuit board 7 so that it can pick up the flexible printed circuit board as a whole by suction. At the slider side end of the suction head 6, there is provided a main head 8 and a sub head 9 independently from each other so that the flexible printed circuit board 7 can be pressed against a load beam 10 and a flexible member 11 with a load and a range that meet respective requirements. A difference in height as small as that of the load beam 10 and the elastic member 11 can be absorbed by this structure.
However, the above described method suffers from the following problem.
That is, in the method in which the flexible printed circuit board 5 is bonded to the head holding member 1 under the condition in which only area A of the flexible printed circuit board 5 is sucked, the portion of the flexible printed circuit board 5 other than area A is dragged, and there is the risk that displacement or deformation such as bending can occur in the flexible printed circuit board 5 while it is moved to the head holding member 1. Even if the dragging does not occur in the portion other than area A, the weight of the flexible printed circuit board 5 will be concentrated at the portion around area A, so that the aforementioned deformation can occur due to this stress concentration. Furthermore, in magnetic heads in recent years, strict precision in bonding is required not only at the slider side but also at the other side from the view point of improvement in facility of assembling. In view of this, it is difficult to achieve alignment of the aforementioned other end by a process of suction applied only to area A, and specifications required by the market cannot be achieved.
On the other hand, in the case of the suction head 6 that can pick up the flexible printed circuit board 7 as a whole, although precision in bonding of both end portions of the flexible printed circuit board can be ensured, there is another problem in that establishment of suction depends on the shape of the head holding member 12.
Specifically, the aforementioned suction head 6 can press a flexible printed circuit board against a load beam 2 having a flat shape as shown in FIG. 6, but such cannot press a flexible printed circuit board against a load beam 13 having a non-flat bonding surface in the form of a bent portion 14 as shown in FIG. 8.
One method that was conceived was to bend a flexible printed circuit board in a tray precedently in such a way as to be kept away from the step of the head holding member and bonding it to the head holding member while keeping that state. However, this method is not practical, since there is the risk that the flexible printed circuit board can be deformed by the aforementioned bending.